1. Field of the Invention
The invention is generally related to a sound generation approach that generates spatial sounds in a listening room. In particular, the invention relates to modeling with only a few user input parameters the listening room responses for a two-channel audio input based upon adjustable real-time parameters without coloring the original sound.
2. Related Art
The aim of a high-quality audio system is to faithfully reproduce a recorded acoustic event while generating a three-dimensional listening experience without coloring the original sound, in places such as a listening room, home theater or entertainment center, personal computer (PC) environment, or automobile. The audio signal from a two-channel stereo audio system or device is fundamentally limited in its ability to provide a natural three-dimensional listening experience, because only two frontal sound sources or loudspeakers are available. Phantom sound sources may only appear along a line between the loudspeakers at the loudspeaker's distance to the listener.
A true three-dimensional listening experience requires rendering the original acoustic environment with all sound reflections reproduced from their apparent directions. Current multi-channel recording formats add a small number of side and rear loudspeakers to enhance listening experience. But, such an approach requires the original audio media to be recorded or captured from each of the multiple directions. However, two-channel recording as found on traditional compact discs (CDs) is the most popular format for high-quality music today.
The current approaches to creating three-dimensional listening experiences have been focused on creating virtual acoustic environments for hall simulation using delayed sounds and synthetic reverb algorithms with digital filters. The virtual acoustic environment approach has been used with such devices as headphones and computer speakers. The synthetic reverb algorithm approach is widely used in both music production and home audio/audio-visual components such as consumer audio/video receivers (AVRs).
In FIG. 1, a block diagram 100 illustrating an example of a listening room 102 with a traditional two-channel AVR 104 is shown. The AVR 104 may be in signal communication with a CD player 106 having a two-channel stereo output (left audio channel and a right audio channel), television 108, or other audio/video equipment or device (video recorders, turntables, computers, laser disc players, audio/video tuners, satellite radios, MP3 players). Audio device is being defined to include any device capable of generating two-channel or more stereo sound, even if such a device may also generate video or other signals.
The left audio channel carries the left audio signal and the right audio channel carries the right audio signal. The AVR 104 may also have a left loudspeaker 110 and a right loudspeaker 112. The left loudspeaker 110 and right loudspeaker 112 each receive one of the audio signals carried by the stereo channels that originated at the audio device, such as CD player 106. The left loudspeaker 110 and right loudspeaker 112 enables a person sitting on sofa 114 to hear two-channel stereo sound.
The synthetic reverb algorithm approach may also be used in AVR 104. The synthetic reverb algorithm approach uses tapped delay lines that generate discrete room reflection patterns and recursive delay networks to create dense reverb responses and attempts to generate the perception of a number of surround channels. However, a very high number of parameters are needed to describe and adjust such an algorithm in the AVR to match a listening room and type of music. Such adjustments are very difficult and time-consuming for an average person or consumer seeking to find an optimum setting for a particular type of music. For this reason, AVRs may have pre-programmed sound fields for different types of music, allowing for some optimization for music type. But, the problem with such an approach it the pre-programmed sound fields lack any optimization for the actual listening room.
Another approach to generate surround channels from two-channel stereo signals employs a matrix of scale factors that are dynamically steered by the signal itself. Audio signal components with a dominant direction may be separated from diffuse audio signals, which are fed to the rear generated channels. But, such an approach to generating sound channels has several drawbacks. Sound sources may move undesirably due to dynamic steering and only one dominant, discrete source is typically detected. This approach also fails to enhance very dryly recorded music, because such source material does not contain enough ambient signal information to be extracted.
Along with the foregoing considerations, the known approaches discussed above for generation of surround channels typically add “coloration” to the audio signals that is perceptible by a person listening to the audio generated by the AVR 104. Therefore, there is a need for an approach to processing stereo audio signals that filters the input channels and generates a number of surround channels while allowing a user to control the filters in a simple and intuitive way in order to optimize their listening experience.